Diabetes is one of lifestyle-related diseases with the background of change of eating habit and lack of exercise. Hence, diet and exercise therapies are performed in patients with diabetes. Furthermore, when its sufficient control and continuous performance are difficult, drug treatment is simultaneously performed. In addition, it has been confirmed by large-scale clinical trial that it is necessary to practice a long-term strict control of blood sugar level so as to prevent patients with diabetes from occurring and advancing diabetic complications by receiving treatment (for example, see the following References 1 and 2). Furthermore, many epidemiologic studies on impaired glucose tolerance and macroangiopathy show that impaired glucose tolerance as the boundary type is also a risk factor in macroangiopathy as well as diabetes. Thus, needs to improve postprandial hyperglycemia have been focused (for example, see the following Reference 3).
In recent years, development of various antidiabetic agents has been progressing with the background of a rapid increase of patients with diabetes. For example, Antidiabetic agents such as biguanides, sulfonylureas, insulin sensitivity enhancers, α-glucosidase inhibitors and the like have been employed. However, biguanides and sulfonylureas show occasionally adverse effects such as lactic acidosis and hypoglycemia, respectively. Insulin sensitivity enhancers show occasionally adverse effects such as edema, and are concerned for advancing obesity. In addition, α-glucosidase inhibitors, which delay carbohydrate digestion and absorption at the small intestine, are used to improve postprandial hyperglycemia. It has been also reported that acarbose, one of α-glucosidase inhibitors, has an effect of preventing or delaying the incidence of diabetes by applying to patients with impaired glucose tolerance (for example, see the following Reference 4). However, since α-glucosidase inhibitors do not affect elevated glucose levels by ingesting a monosaccharide of glucose (for example, see the following Reference 5), with recently changing compositions of sugars in meals, a wider range of activities inhibiting carbohydrate absorption has been desired.
In recent years, research and development of new type antidiabetic agents have been progressing, which promote urinary glucose excretion and lower blood glucose level by preventing reabsorption of excess glucose at the kidney (for example, see the following Reference 6). In addition, it is reported that SGLT2 (sodium-dependent glucose transporter 2) is present in the S1 segment of the kidney's proximal tubule and participates mainly in reabsorption of glucose filtrated through glomerular (for example, see the following Reference 7). Accordingly, inhibiting a human SGLT2activity prevents reabsorption of excess glucose at the kidney, subsequently promotes excreting excess glucose though the urine, and normalizes blood glucose level. In addition, since such agents for promoting the excretion of urinary glucose excrete excess glucose though the urine and consequently the glucose accumulation in the body is decreased, they are also expected to have a preventing or alleviating effect on obesity and a diuretic effect. Furthermore, the agents are considered to be useful for various related diseases which occur accompanying the progress of diabetes or obesity due to hyperglycemia.
Furthermore, it has been known that SGLT1, sodium-dependent glucose transporter 1, exists in the small intestine which controls carbohydrate absorption. It has been also reported that insufficiency of glucose and galactose absorption arises in patients with dysfunction due to congenital abnormalities of human SGLT1 (for example, see the following References 8-10). In addition, it has been confirmed that SGLT1 is involved in glucose and galactose absorption (for example, see the following References 11 and 12). Furthermore, it is confirmed that mRNA and protein of SGLT1 increase and absorption of glucoses are accelerated in OLETF rats and rats with streptozotocin-induced diabetic symptoms (for example, see the following References 13 and 14). Generally in patients with diabetes, carbohydrate digestion and absorption are increased. For example, it is confirmed that mRNA and protein of SGLT1 are highly increased in the human small intestine (for example, see the following Reference 15). Therefore, blocking a human SGLT1 activity inhibits absorption of carbohydrates such as glucose at the small intestine, subsequently can prevent increase of blood sugar level. Especially, it is considered that delaying glucose absorption based on the above mentioned mechanism is effective to normalize postprandial hyperglycemia.
Therefore, fast development of antidiabetic agents with novel action mechanism, which have an inhibitory activity in human SGLT, has been desired to improve or solve the above-mentioned problems.
Fused heterocyclic derivatives provided in the present invention are entirely novel compounds. It has not ever been reported that these derivatives have an inhibitory activities in SGLT1 and/or SGLT2 and inhibit absorption of glucose and galactose at the small intestine, or are useful as agents to inhibit reabsorption of excess glucose at the kidney.    Reference 1: The Diabetes Control and Complications Trial Research Group, N. Engl. J. Med., 1993.9, Vol.329, No. 14, pp. 977-986;    Reference2: UK Prospective Diabetes Study Group, Lancet, 1998.9, Vol.352, No. 9131, pp. 837-853;    Reference 3: Makoto TOMINAGA, Endocrinology & Diabetology, 2001.11, Vol.13, No. 5, pp. 534-542;    Reference 4: Jean-Louis Chiassonand5persons, Lancet, 2002.6, Vol.359, No. 9323, pp. 2072-2077;    Reference 5: Hiroyuki ODAKA and 3 persons, Journal of Japanese Society of Nutrition and Food Science, 1992, Vol.45, p. 27;
Reference 6: Luciano Rossetti and 4 persons, J. Clin. Invest., 1987.5, Vol.79, pp. 1510-1515;    Reference 7: Yoshikatsu Kanai and 4 persons, J. Clin. Invest., 1994.1, Vol.93, pp. 397-404;    Reference 8: Tadao BABA and 1 person, Supplementary volume of Nippon Rinsho, Ryoikibetsu Shokogun, 1998, No. 19, pp. 552-554;    Reference 9: Michihiro KASAHARA and 2 persons, Saishin Igaku, 1996.1, Vol.51, No. 1, pp. 84-90;    Reference 10: Tomofusa TSUCHIYA and 1 person, Nippon Rinsho, 1997.8, Vol.55, No. 8, pp. 2131-2139;    Reference 11: Yoshikatsu KANAI, Kidney and Dialysis, 1998.12, Vol.45, extra edition, pp. 232-237;    Reference 12: E. Turk and 4 persons, Nature, 1991.3, Vol.350, pp. 354-356;    Reference 13: Y. Fujitaand5persons, Diabetologia, 1998, Vol.41, pp. 1459-1466;    Reference 14: J. Dyer and 5 persons, Biochemical Society Transactions, 1997, Vol.25, p. 479S;    Reference 15: J. Dyer and 4 persons, American Journal of Physiology, 2002.2, Vol.282, No. 2, pp.G241-G248